KNOWLEDGE AREA: Diversity, change and continuity TOPIC 1: Biodiversity of Plants and Reproduction

Biodiversity of Plants

Orchids

Introduction to Plant Kingdom

The Bryophytes

The Pteridophytes

The Gymnosperms

The Angiosperms

The Progressive Development of Land Plants

All the plants in the plant kingdom maybe grouped into vascular and non-vascular plants.

Vascular plants are those with conducting tissue.

Non-vascular plants are those that do not have conducting tissue.

Do you remember that conducting tissue are xylem and phloem?

Some examples of non-vascular plants are mosses, liverworts and hornworts.

These plants belong to the Phylum Bryophyta.

The vascular plants may be further divided into those that bear seeds and those that do not.

An example of seedless plants are the ferns.

Pine tree and flowering plants are examples of seed-bearing plants.

The ferns belong to the Phylum Pteridophyta.

While the pine plant belongs to the Phylum Gymnosperm and the flowering plants belong to the Phylum Angiosperm.

All plants have a lifecycle that is made up of 2 generations.

These 2 generations are the:

1. Gametophyte

2. Sporophyte

These generations alternate with each other.

One generation gives rise to the other.

You will learn more about this in grade 12.

This group is made up of 3 large groups.

They are the: a. Mosses b. Liverworts c. Hornworts All these are

terrestrial plants. They grow in damp,

shady ground.

liverwort

hornwort

The most well known bryophyte is the moss.

In the bryophytes the dominant generation is the gametophyte.

The gametophyte is dominant because it lives longer and is larger than the sporophyte generation. The moss showing the 2

generations

The plant has root-like structures called rhizoids.

The rhizoids anchor the plant to the ground.

The moss also has stem-like and leaf-like structures.

Since the moss has no true roots, stems and leaves it is called a

thallus.

Moss-gametophyte

The moss also lacks xylem and phloem.

Therefore we say it lacks conducting tissue.

They reproduce using

spores and have no seeds.

These spores occur in spore bearing capsules, therefore the

moss has no fruits.

Moss showing the

sporophyte

Spore bearing

capsule

The male and female reproductive organs are found on different branches of the same plant.

The sperms have to move from the male reproductive organs to the female reproductive organs.

The sperms swim to reach the egg in the female reproductive organ.

The sperms swim in a film of water to reach the egg.

Therefore we say that the moss is

dependent on water for reproduction.

During asexual reproduction spores are produced.

These spores are dispersed by wind.

The moss is dependent on dry weather for

the release and dispersal of spores.

This phylum includes the ferns, horsetails and whisk ferns.

fern

Horsetail

fern

Whisk fern

These plants have vascular tissue.

They also have supporting tissue.

They therefore have true roots, stems and leaves.

The Pteridophytes are not thallus plants.

They reproduce using spores, they do not produce seeds.

Spores are made and stored in spore bearing capsules.

They do not have fruits.

They undergo both sexual and asexual reproduction.

The sperms need to swim to reach the egg in the female reproductive organ.

The sperm swims in water.

Therefore the pteridophytes depend on water for sexual reproduction.

During asexual reproduction spores are produced.

These spores depend on dry weather for their release and dispersal.

The dominant generation is the sporophyte generation.

The sporophyte generation is dominant because it is able to stay alive and produce spores for many cycles.

The gametophyte generation dies after just one cycle of gamete formation and fertilization.

All plants that bear seeds belong to the phylum Spermatophyta.

These plants maybe separated into 2 groups,

those that bear naked seeds and those whose seeds occur within fruit.

The plants that produce naked seeds belong to the group Gymnosperms.

The plants that produce seeds within fruits belong to the group Angiosperms.

There are 4 groups of Gymnosperms.

These 4 groups are:-

1. Conifers

2. Cycads

3. Gnetophytes

4. Ginkgophytes

1. The Conifers: These are cone

bearing plants. They are made up of

about 600 different species.

This makes them the biggest group of gymnosperms.

Some examples are pine trees, yellow woods, red woods and firs.

A selection of Conifers

2. The Cycads: They form the second

largest group of gymnosperms.

They are made up of 130 extant species.

Extant means that the organism is not extinct.

There were a much larger population of cycads but many of them became extinct.

Cycads

3. The Gnetophytes:

This group is very small.

It is made up of only 3 genera. (Genera is plural of genus)

One example is the Welwitschia mirabilis, that is found in the Namib Desert.

Welwitschia mirabilis

4. The Ginkgophytes:

This group is made up of only one species.

This species is called the Ginkgo biloba.

The Ginkgo biloba is commonly known as the maidenhair tree.

Maidenhair tree

These plants have conducting tissue, therefore water and manufactured food can be transported to all parts of the plant.

They also have supporting tissue, they have enough strength and support to allow them to grow to great lengths.

They have true roots, stems and leaves.

Therefore they are not thallus plants.

They undergo both sexual and asexual reproduction.

During sexual reproduction seeds are produced.

These seeds are found on the cones.

They do not bear fruit.

They have spores, but they have both male and female spores.

These spores are inside the pollen grain and ovary.

They are not dependent on water for reproduction.

The male spores are carried to the female cone by the wind.

The pollen tube then carries the spores to the ovary.

Two generations also occur in these plants.

The sporophyte generation is dominant.

The gametophyte generation is separated into a male gametophyte and a female gametophyte.

Both the male and female gametophyte generation occur within the sporophyte.

These are terrestrial plants, that occur over a widespread area.

They are a very successful group of plants.

Some of them occur in very dry areas, these are called xerophytes.

Other angiosperms are found in areas that have an abundant water supply, these plants are called hydrophytes.

Then finally some of them live in areas of moderate water supply, such plants are called mesophytes.

These plants also have both the sporophyte and gametophyte generations.

The sporophyte is the dominant generation.

Two separate gametophyte generations occur.

They are the male gametophyte and the female gametophyte.

Both these gametophyte generations occur in the sporophyte generation.

STRUCTURE:

The sporophyte generation is the flowering plant.

It is made up of roots, stems leaves and flowers.

Two types of roots systems may occur.

These are the tap root system or the adventitious root system.

These stems are upright structures.

They are found above the ground.

They bear leaves and flowers.

The portion of the stem from which the leaf and sometimes flowers arises is called the node.

The part between two nodes is called the internodes.

These stems have conducting tissue.

They can also be quite tall and therefore the have well developed supporting and strengthening tissue.

The strengthening tissue maybe collenchyma or sclerenchyma.

FUNCTION

The stem holds the flower in a perfect position for pollination.

The stem holds the leaves in a perfect position to receive sunlight.

The stem also transports water and mineral salts from the roots to the leaves.

They also transport manufactured food from the leaves to all parts of the plant.

Therefore it has well developed xylem and phloem.

STRUCTURE: The leaves are green

in colour. They can be broad

and flat as in the dicot leaf or long and narrow in the monocot leaf.

Dicot leaves have net venation while monocot leaves have parallel venation.

Monocot leaf Dicot leaf

The flower is the reproductive organ of the plant.

The male and female gametophyte are found in the flower.

The male and female gametes are found within the male and female gametophyte.

In the dicot flower the perianth is differentiated into 2 whorls.

These are the corolla (petals) and the calyx (sepals)

Dicot Flower

In the monocot flower the calyx and corolla is fused to form the perigone.

Monocot Flower

Stamen – male spores – produced in pollen

sacs

Pistil – style and ovary – is female sex organ

Ovule – located inside the ovary

Pollination

A ripe pollen grain lands on a receptive stigma.

Grain germinates and develops a pollen tube

with 2 male gametes (male gametophyte)

One female spore (in the ovule) forms the

embryo sac(female gametophyte)

Pollination continue

the embryo sac contains an ovum and 2 polar

nuclei

Pollen tube grows down the style, into the ovary

and penetrates the ovule – releases male

gametes

One gamete fuses with ovum – forms a zygote

Zygote becomes embryo

Fertilised ovule develops into seed that contains

embryo endosperm and testa

Seed germinates – testa ruptures